ABSTRACT Surgical bypass grafting using autologous veins is the cornerstone therapy for coronary artery disease (CAD) and occlusive peripheral artery disease (PAD). However, 30-50% of lower extremity vein grafts and >50% of coronary artery bypass grafts (CABG) fail within 5 and 10 years, respectively. Medical therapies to control co- morbidities (diabetes/dyslipidemia), inhibit platelet aggregation, decrease inflammation, and reduce smooth muscle cell (SMC) proliferation, only provide a modest benefit in reducing CABG failure and in-stent restenosis, but there has been no corresponding benefit in lower extremity vein bypass grafts. Mid-term vein graft failure, ranging from 3 to 24 months, accounts for >70% of failures and is primarily due to intimal hyperplasia (IH). Based on a better understanding of the pathophysiology of IH, we propose that its prevention will be best achieved by 1) maintaining endothelial cell (EC) anti-inflammatory and anti-thrombotic properties and protecting them from apoptosis, 2) reducing SMC activation, migration and proliferation, and 3) enhancing EC growth to improve lumen re-endothelialization, 4) while promoting death of intimal SMC to shrink pre-existing lesions. Our previous in vitro work in human coronary artery EC and SMC, and in mouse, rat and recently rabbit animal models of vascular disease, suggest that overexpression of the potent NF-?B inhibitory protein, A20, may be ideal to prevent vein graft failure. A20 fulfills all of the above criteria, including protecting EC from apoptosis while promoting apoptosis of intimal SMC. Our loss-of-function studies demonstrating aggravated lesions of transplant arteriosclerosis in aortic mouse allografts with partial A20 knockdown further support the physiologic protective role of A20 against IH. This bears clinical relevance, since recently identified A20 single nucleotide polymorphisms (SNPs) that decrease A20 mRNA levels were correlated with 3-fold increased incidence of CAD in diabetics. Our aim is to provide proof-of-principle/mechanistic studies supporting A20's ability to prevent IH in vein grafts, using a pre-clinical canine model that mimics vein graft failure patterns observed in patients. Specifically, we developed a novel, efficient and clinically safe vasculotropic vector to bioengineer canine veins with A20, and test its impact on IH, stenosis, and thrombosis in an reversed autologous cephalic vein (CV) to common femoral artery (CFA) lower extremity vein bypass interposition graft in canines. A successful outcome of this high-risk/high-impact exploratory study would incentivize us to pursue and optimize vascular A20-based therapies for timely clinical translation.